Field of the Invention
The invention relates to a circuit arrangement for level conversion of binary signals in a control system for a printing-technology machine, in particular, a printing press. In order to control operating procedures of a machine in the field of printing technology, a multiplicity of actuators and sensors are provided which interact with one or more control circuits. If binary signals are transmitted line-bound between the actuators or sensors and a control circuit, then the binary signals are expressed by DC voltage values which are generated by electronic components of a driver circuit. On account of the unavoidable component tolerances and a desired interference immunity, a low level or L level and a high level or H level are defined as the binary signal values (0; 1), the H level lying in a range above an upper threshold value and the L level lying in a range below a lower threshold value. The range between upper and lower threshold values corresponds to no binary signal value (0; 1). Driver circuits and receiver circuits operate either according to the principle of so-called positive logic, in which case the binary signal value (1) is defined by the H level, or according to the principle of negative logic, in which case the binary signal value (1) is defined by the L level. In order to ensure the interaction of the actuators or sensors with the control circuit, the binary signal values (0; 1) must correspond to the desired levels. In order to increase the flexibility in the controllers and the connected actuators or sensors, it has been known heretofore to provide additionally inverted inputs and outputs, respectively, for inputs and outputs, with the result that it is optionally possible to operate in positive or negative logic. Faulty circuits cannot be precluded in this case, in particular when an element is to be renewed on the control circuit side or on the actuator/sensor side. In order to reduce the probability of faulty circuits, it is possible to resort to compatible elements of one and the same property, which have to be available in stock and should, as much as possible, originate from the same manufacturer. At the output, driver circuits have an electrical switching element which, when it is driven, generates an H or L level at the output. In this regard, embodiments are possible wherein the switching element establishes a low-impedance connection to a positive operating voltage source or to the zero potential of the operating voltage source. In further different embodiments, the switching elements are connected to resistors. In the case of push-pull output stages, two electrical switching elements act at the output, the switching elements being able to connect the output in a low-impedance manner both with respect to the positive operating voltage source and with respect to the zero potential or a negative operating voltage source. In addition to the switching elements described hereinbefore, which, at the output, set DC voltage values corresponding to the binary signal values (0; 1), driver circuits are known which have switchable current sources in addition to the output stage.